Add PIC-level support to Clang.

[jhibbits]

Summary

This distinguishes between -fpic and -fPIC now, with the additions in LLVM for
PIC level support.

[jhibbits]

ParseStmtAsm.cpp was missing, fix that as well.

[• rafael]

lib/CodeGen/BackendUtil.cpp

428 ↗

(On Diff #14425)

Don't you want to produce an error if -pic-level is not 1 or 2?

[jhibbits]

Update to use the Module PIC Level API.

[• rafael]

lib/CodeGen/CodeGenModule.cpp

401

We use llvm_unreachble instead of assert(0).

[jhibbits]

lib/CodeGen/CodeGenModule.cpp

401

d'oh, fail :(

[jhibbits]

Use llvm_unreachable() instead of assert(0).

[• rafael]

LGTM with a nit.

lib/CodeGen/CodeGenModule.cpp

395

You can fold the variable declaration into the if:

if (uint32_t PLevel = Context.getLangOpts().PICLevel) {

[rnk]

lib/CodeGen/BackendUtil.cpp

428 ↗

(On Diff #14425)

It's too easy for the user to try to do something like clang -cc1 -pic-level 3 t.c and crash the compiler with assert or llvm_unreachable. We should either clamp the level to [0-2] or issue a diagnostic in lib/Frontend/CompilerInvocation.cpp.

[jhibbits]

Thanks for the review, Rafael!

lib/CodeGen/CodeGenModule.cpp

395

That may be legal C++, but it makes me really uncomfortable, and makes it (trivially, I guess) less readable, I think.

[jhibbits]

Closed by commit rL222227 (authored by @jhibbits).

[• rafael]

rafael wrote:

Don't you want to produce an error if -pic-level is not 1 or 2?

It's too easy for the user to try to do something like clang -cc1 -pic-level 3 t.c and crash the compiler with assert or llvm_unreachable. We should either clamp the level to [0-2] or issue a diagnostic in lib/Frontend/CompilerInvocation.cpp.

I don't think -cc1 options are considered user visible. Having another
value in here means a bug somewhere else in clang.

Cheers,
Rafael

lib/CodeGen/CodeGenModule.cpp

uint64_t WCharWidth =
         Context.getTypeSizeInChars(Context.getWideCharType()).getQuantity();
     getModule().addModuleFlag(llvm::Module::Error, "wchar_size", WCharWidth);
 
     // The minimum width of an enum in bytes
     uint64_t EnumWidth = Context.getLangOpts().ShortEnums ? 1 : 4;
     getModule().addModuleFlag(llvm::Module::Error, "min_enum_size", EnumWidth);
   }
 
+  uint32_t PLevel = Context.getLangOpts().PICLevel;
+  if (PLevel) {
+    llvm::PICLevel::Level PL = llvm::PICLevel::Default;
+    switch (LangOpts.PICLevel) {
+    case 0: break;
+    case 1: PL = llvm::PICLevel::Small; break;
+    case 2: PL = llvm::PICLevel::Large; break;
+    default: llvm_unreachable("Invalid PIC Level");
+    }
+
+    getModule().setPICLevel(PL);
+  }
+
   SimplifyPersonality();
 
   if (getCodeGenOpts().EmitDeclMetadata)
     EmitDeclMetadata();
 
   if (getCodeGenOpts().EmitGcovArcs || getCodeGenOpts().EmitGcovNotes)
     EmitCoverageFile();
 

test/CodeGen/piclevels.c

+// RUN: %clang_cc1 -emit-llvm -pic-level 2 %s -o - | FileCheck %s -check-prefix=CHECK-BIGPIC
+// RUN: %clang_cc1 -emit-llvm -pic-level 1 %s -o - | FileCheck %s -check-prefix=CHECK-SMALLPIC
+
+// CHECK-BIGPIC: !llvm.module.flags = !{{{.*}}}
+// CHECK-BIGPIC: !{{[0-9]+}} = metadata !{i32 1, metadata !"PIC Level", i32 2}
+// CHECK-SMALLPIC: !llvm.module.flags = !{{{.*}}}
+// CHECK-SMALLPIC: !{{[0-9]+}} = metadata !{i32 1, metadata !"PIC Level", i32 1}